Whooping cough bacterium is evolving
Research led by the University of New South Wales (UNSW) has found that the bacterium that causes whooping cough, Bordetella pertussis, has changed - most likely in response to the vaccine used to prevent the disease. The study has been published in the journal Emerging Infectious Diseases.
The researchers analysed strains of B. pertussis from across Australia and found that many strains no longer produce a key surface protein called pertactin - one of the three proteins, made from purified extracts of B. pertussis bacteria, which are present in the vaccine currently used in Australia. The acellular vaccine was introduced in 1997 to replace the previous whole-cell vaccine, after side effects such as fever and crying dissuaded many parents from having their children vaccinated.
During 2008-2012, a large outbreak of whopping cough occurred, with 142,000 cases around Australia. The researchers analysed 320 bacteria samples obtained from patients with whooping cough during this period and found that the proportion of pertactin-free bacteria rose from 5% of cases in 2008 to 78% in 2012. On average, 30% of B. pertussis isolates did not express pertactin.
“It’s like a game of hide and seek,” said senior author Associate Professor Ruiting Lan, of the UNSW School of Biotechnology and Biomolecular Sciences. “It is harder for the antibodies made by the body’s immune system in response to vaccination to ‘search and destroy’ the whooping cough bacteria which lack pertactin.
“This could mean that these pertactin-free strains have gained a selective advantage over bacterial strains with the pertactin protein.”
Pertactin-free strains have also been detected overseas, in countries such as France and the United States. According to Associate Professor Lan, “The fact that they have arisen independently in different countries suggests this is in response to the vaccine.”
There is no evidence that the pertactin-free strains are more harmful than other strains, and it is not yet clear whether they reduce the effectiveness of the vaccine in the short or long term. “More studies are needed to better understand the effects of vaccination on the evolution of the organism,” said Associate Professor Lan.
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